Why your workouts make you sick

Because it's damn hard to do your long run with a head cold.

It’s a frustrating characteristic of high-level fitness: In the midst of training diligently—for, say, a marathon or an Ironman—you get sick more than ever. Which is odd because you ought to be in the best shape of your life. That’s because an intense exercise regimen seems to suppress the immune system, making athletes more prone to minor respiratory infections such as colds and flu.

Here’s why: Hardcore training appears to increase the stress hormone cortisol in the body, which suppresses the immune system, making germ attacks harder to fight off. Those repeated colds can snowball, disrupting training and impacting performance and recovery.

“The volume of exercise that depresses immunity sufficiently to increase risk of infection will differ depending on fitness, diet and pathogen exposure, but certainly both recreational and elite athletes are susceptible,” says Michael Gleeson, retired professor of sport, exercise and health sciences at Loughborough University in the UK.

But you can bypass illness related to prolonged bouts of exercise (generally, intense training for at least 90 minutes, five or more days a week) by amending your eating. Here’s what’s thought to work to stave off sickness while you’re training.


Without adequate carbohydrates to fuel your workouts, bodily proteins may be broken down to supply energy, which can tax the immune system, says Cynthia Sass, a registered dietitian and board-certified specialist in sports dietetics. Carbohydrate intake during exercise also maintains blood glucose and lowers stress hormone levels, which also help prevent immune stress.

“A good rule of thumb for carbohydrates during intense exercise is to consume 30 to 60 grams per hour,” says Cynthia Sass, RD, a New York-based dietitian. Those carbs can come from a sports drink, or easy-to-digest foods such as certain bars, dried fruits or gels, along with water, she says.


“Exercise results in bodily wear and tear, and post-exercise, the body is primed for healing,” says Sass. “Protein consumed after working out provides the amino acid building blocks needed for recovery, including repair of muscle, as well as maintenance of the immune system.”

Aim for 20 to 30 grams of protein post-workout (from fish or meat, or vegetarian sources such as chickpeas or yogurt) for immune recovery and training adaptation, Gleeson says.


Getting a plethora of micronutrients is essential to maintaining good health, athlete or not, Gleeson says. But vitamin D seems to be particularly important in preventing illness during training. Low levels of vitamin D have been associated with increased respiratory infection risk. “Useful daily supplements include vitamin D3 in winter (1000 IU/day), vitamin C (citrus fruits or up to 1000 mg/day supplement) and probiotics,” he says. (Though before you take any supplements, you should talk to your doctor.)


Ensuring probiotics—those good gut bacteria that can be found in food items such as kefir and kimchi—are apart of athletic diets was associated with improvements in acquired immunity and fewer respiratory infections and gastrointestinal problems, Gleeson concluded. Sass notes that previous research supports his finding. And focusing on prebiotics can help bolster the effects of probiotics, so grab a bunch of radishes and a bundle of asparagus while you're at it.